1. Technical Field
The invention relates to a vibrating reed such as a piezoelectric vibrating reed made of a piezoelectric material, a vibrator, an oscillator, and an electronic device using these components.
2. Related Art
In the past, as the vibrating reed vibrating in a flexural vibration mode or other vibration modes, there is widely used a tuning-fork piezoelectric vibrating reed having a pair of vibrating arms extending in parallel to each other from the base of a substrate made of a piezoelectric material such as a quartz crystal so as to vibrate in a direction in which the vibrating arms come closer to and break away from each other. Miniaturization of the various products to be attached with a vibrating device provided with such a vibrating reed such as small-sized information equipment such as hard disk drives (HDD), mobile computers, or IC cards, mobile communication equipment such as cellular phones, car telephones, or paging systems, or vibratory gyro-sensors has been increasingly advanced, and in accordance therewith the demand for miniaturization of the vibrating devices and the vibrating reeds to be incorporated in the vibrating devices have been further increasing.
Further, as another problem of miniaturization, there can be cited the fact that when exciting the vibrating arms of the vibrating reed, a loss is caused in the vibrational energy, which causes degradation in the performance of the vibrating reed such as increase in the crystal impedance (CI) value or decrease in the Q-value. Therefore, in order for further preventing or reducing the loss of the vibrational energy while achieving the miniaturization of the vibrating reed, various devices have been made in the past. For example, there is known a tuning-fork quartz-crystal vibrating reed provided with an elongate groove on the principal surface of the vibrating arms, and cut sections or cuts (cut grooves) with a predetermined depth formed on both sides of the base from which the vibrating arms extend (see, e.g., JP-A-2002-280870 (Document 1)).
The tuning-fork quartz-crystal vibrating reed described in the Document 1 will specifically be explained with reference to the drawings. FIG. 8 is a plan view schematically showing the tuning-fork quartz-crystal vibrating reed as an example of the vibrating reed of the related art.
In FIG. 8, the tuning-fork quartz-crystal vibrating reed 100 has a base 121 made of a quartz crystal, and a pair of vibrating arms 122 extending in parallel to each other from an end portion of the base 121. Each of the vibrating arms 122 has a pair of principal surfaces of the vibrating arm 122 and a pair of side surfaces connecting the pair of principal surfaces, and further, each of the vibrating arms 122 is provided with a bottomed elongate groove 126 along the longitudinal direction of the vibrating arm 122 with an opening on at least one of the pair of principal surfaces. It should be noted that although not shown in the drawings the area including the elongate groove 126 is provided with an excitation electrode for vibrating the vibrating arm 122.
Further, on the other sides (two sides) in the direction perpendicular to the one end portion of the base 121 from which the vibrating arms 122 extend, there are formed a pair of cuts 141A, 141B in an opposed directions along a single straight line so that a constricted shape appears in both of the principal surfaces of the base 121. The base 121 includes a first portion 121a and a second portion 121b located on both sides across the pair of cuts 141A, 141B, and a connecting portion 121c for connecting the first portion 121a and the second portion 121b between the pair of cuts 141A, 141B. The second portion 121b is provided with an externally-connecting electrode, not shown, used for electrical connection to an external board such as a package. The tuning-fork quartz-crystal vibrating reed 100 is bonded and fixed to the external board such as a package while achieving electrical connection using the second portion 121b of the base 121 as a fixing section.
Since the elongate grooves 126 are respectively provided to the vibrating arms 122, the vibrating arms 122 becomes easy to move and vibrates efficiently, the tuning-fork quartz-crystal vibrating reed 100 has a property that the vibrational loss can be reduced and the CI value can be suppressed to a low level.
Further, in the case in which the vibration of the vibrating arms 122 includes a vertical direction component, the pair of cuts 141A, 141B provided to the base 121 block the transmission of the vibration of the vibration arms 122, and therefore, a so-called vibration leakage, the phenomenon that the vibration is transmitted to the outside via the base 121, is prevented, which exerts the effect of preventing the increase in the CI value, and at the same time, prevents the variation in the CI value between the vibrating arms 122.
However, in the tuning-fork quartz-crystal vibrating reed 100 described in the Document 1, there arises a problem that the cuts 141A, 141B provided to the base 121 might cause degradation of the rigidity of the base 121 to degrade the impact resistance.
Specifically, in the tuning-fork quartz-crystal vibrating reed 100 shown in FIG. 8, when a predetermined drive voltage is applied to the excitation electrode, the vibrating arms 122 vibrate in a horizontal direction indicated by the arrows in the drawing in which the vibrating arms 122 come closer to and break away from each other. If an impact of significantly displacing the vibrating arms 122 in the direction the same as vibration direction is applied to the tuning-fork quartz-crystal vibrating reed 100, large stress is caused locally on the side of the base 121. In other words, if the tip side of each of the vibrating arms 122 is significantly displaced taking the second portion 121b of the base 121 as a fixed end, the stress is concentrated at a tip portion 142A or a tip portion 142B of the cut 141A or the cut 141B corresponding to the opposite side to the direction in which the vibrating arms 122 are displaced out of the pair of cuts 141A, 141B. In particular, since the quartz crystal has low mechanical strength against the tensile stress, if the impact of significantly displacing the vibrating arms 122 to the +X direction (leftward) indicated by the arrow in the drawing is applied to the tuning-fork quartz-crystal vibrating reed 100, for example, large tensile stress is applied at the tip portion 142B of the cut 141B of the base 121 located in the −X direction (rightward) in the drawing, which might cause a crack or breakage.